The word 'sucker' originates from the Old English verb 'sūcan', meaning to draw liquid into the mouth by creating a vacuum. This verb is part of a widespread Germanic family, traceable to the Proto-Indo-European root seug-, meaning to suck. The agent suffix '-er' was added to form a noun for 'one who sucks'. Its earliest literal applications were to young mammals and, later, to specialized organs in animals and plants. The figurative sense of a gullible person, emerging in the 19th century, derives from the metaphor of someone as easily 'drawn in' or deceived as an infant is to a feeding source. This logic connects the physical action of suction to the abstract concept of being easily influenced or duped.

Structure: suck + er suck: From Old English 'sūcan' (to suck), of Germanic origin. It functions as the core verb root denoting the action of drawing in. er: A Germanic agent noun suffix, used to form nouns denoting a person or thing that performs the action of the verb.